This invention relates to a digital multiplexed wireless apparatus (SDH wireless transmission apparatus) using microwaves in an SDH (Synchronous Digital Hierarchy) network. More particularly, the invention relates to an SDH wireless apparatus, which has a plurality of working lines and at least one standby line, for sending and receiving wireless signals in which STM (Synchronous Transfer Mode) signals are used as baseband signals.
An SDH wireless transmission apparatus tends to have a large amount of hardware owing to the size of its transmission capacity. There is increasing need to reduce the size and cost of such apparatus.
In addition, demand for integrated supervision of wireless transmission apparatus and equipment such as optical transmitters and switches has grown in recent years. In SDH communication networks, supervisory control systems are being standardized in accordance with ITU-T and other recommendations, and the need for integrated supervision that is not media-dependent is growing year by year.
In SDH network management, moreover, there is a need for consolidated management of communication devices supplied by a plurality of vendors. However, SDH networks employ additional signals referred to as SOH (Section Overhead) and, though methods of using SOH are being decided by ITU-T, etc., whether or not SOH is used and methods of using SOH differ subtly from one manufacturer to another. As a consequence, an expedient sometimes adopted is to change the way overhead is used as by setting the method of use, thereby making it possible to deal with equipment manufactured by multiple vendors. However, the setting of the equipment and the method of use become more complicated and cost rises. The present invention concerns an SDH wireless transmission apparatus that addresses these difficulties.
The application of SDH techniques in networks is progressing especially in the field of optical transmission. There are cases in which such an SDH communications network incorporates wireless transmission channels. For example, in a case where an SDH communications network is constructed across the ocean or across steep mountainous areas, an optical cable must be laid on the ocean floor or across mountainous terrain. However, the work for laying such cables is a major undertaking and requires great expenditures. When an SDH communications network is constructed in areas where the laying of cable is difficult, as in the case of the ocean floor or steep mountain ranges, an optical transmission line is laid as far as the entrance to the area, an optical transmission line is laid from the exit of the area and a wireless transmission path (channel) is introduced between these two optical transmission lines.
FIG. 19 illustrates an example of the arrangement of an SDH network in which a wireless transmission path is introduced into an optical transmission line. Transmission is performed upon terminating the redundant lines of the optical transmission path. The network includes optical transmission units 1a, 1b and wireless units 2a, 2b. Optical transmission lines 3.sub.1W.about.3.sub.2P are laid between the optical transmission unit 1a and the wireless unit 2a. The optical transmission lines 3.sub.1W, 3.sub.2W are working channels, and the optical transmission lines 3.sub.1P, 3.sub.2P are protection (i.e., standby) channels. The protection channels 3.sub.1P, 3.sub.2P become working channels when failures develop in the working channels 3.sub.1W, 3.sub.2W, respectively. Identical data is transmitted on the working channels and protection channels.
Numerals 4.sub.1W, 4.sub.2W denote wireless working channels provided to correspond to the optical working channels 3.sub.1W, 3.sub.2W, respectively. Numeral 4.sub.P represents one wireless protection channel. The wireless unit 2a terminates the optical protection channels and transmits data from the optical working channels 3.sub.1W, 3.sub.2W to the opposing wireless unit 2b via the wireless working channels 4.sub.1W, 4.sub.2W. Further, when a failure has developed in one of the wireless working channels 4.sub.1W, 4.sub.2W, the wireless unit 2a transmits data, which has been accepted from the corresponding optical working channel, to the wireless unit 2b via the wireless protection channel 4.sub.P, thereby relieving the failed wireless working channel.
Optical transmission lines 5.sub.1W.about.5.sub.2P are laid between the wireless unit 2b and the optical transmission unit 1b. The optical transmission lines 5.sub.1W, 5.sub.2W are working channels, and the optical transmission lines 5.sub.1P, 5.sub.2P are protection channels. The protection channels 5.sub.1P, 5.sub.2P become the working channels when failures develop in the working channels 5.sub.1W, 5.sub.2W, respectively. The wireless unit 2b sends the optical working channel 5.sub.1W and the optical protection channel 5.sub.1P data accepted from the first wireless working channel 4.sub.1W or wireless protection channel 4.sub.P (at the time of failure), and sends the optical working channel 5.sub.2W and the optical protection channel 5.sub.2P data accepted from the second wireless working channel 4.sub.2W or wireless protection channel 4.sub.P (at the time of failure). As a result, identical data is transmitted to the optical working channels and optical protection channels.
In FIG. 19, an optical working channel and an optical protection channel form a pair, and two of such pairs are provided. However, N (.gtoreq.2) pairs are provided ordinarily. More specifically, the optical channels consist of N pairs of optical working channels and optical protection channels. The wireless channels have wireless working channels corresponding to the N-number of optical working channels as well as one wireless protection channel.
FIG. 20 is a diagram for describing the structure of a frame in SDH. This is for a transmission rate of 155.52 Mbps. One frame is composed of 9.times.270 bytes. The first 9.times.9 bytes constitute section overhead (SOH), and the remaining bytes constitute path overhead (POH) and payload (PL).
Section overhead SOH transmits information (a frame synchronizing signal) representing the beginning of the frame, information specific to the transmission line (namely information which checks for error at transmission time, information for network maintenance, etc.) and a pointer indicating the position of the path overhead POH. Path overhead POH transmits end-to-end supervisory information within a network. The payload PL is a section which transmits 150-Mbps information.
The section overhead SOH is composed of regenerator section overhead of 3.times.9 bytes, a pointer of 1.times.9 bytes and multiplex section overhead of 5.times.9 bytes. As shown in FIG. 21, the multiplex section is the section between terminal repeater units 11, 12. In a case where a number of transmission lines 13a.about.13c and repeaters 14a, 14c are provided between the terminal repeater units 11, 12, the regenerator section is the section between both ends of one transmission line, and the multiplex section is composed of a plurality of regenerator sections.
As shown in FIG. 22, the regenerator section overhead has bytes A1.about.A2, C1, B1, E1, F1, D1.about.D3, and the multiplex section overhead has bytes B2, K1.about.K2, D4.about.D12, S1, Z1.about.Z2. The meaning of each byte is illustrated in FIG. 23. The regenerator section overhead and multiplex section overhead have a number of undefined bytes. Use of these bytes is left to the communications manufacturer concerned.
The K1 byte among the overhead bytes is used mainly to request switching and designates the level of the switch request and the switched line. The K2 byte is used mainly to respond to the K1 byte and indicates whether the system is 1:1 or 1:N (number of working channels with respect to one protection channel), the type of changeover mode, content of a failure, etc. There are two types of switching modes, namely a unidirectional mode, in which only a signal in one direction is changed over, and a bidirectional mode, in which signals in both directions are changed over simultaneously.
FIGS. 24A, 24B are diagrams useful in describing switching sequences using the K1, K2 bytes. In the case of the unidirectional mode, the K1 byte (switch request) is sent to a station A if a station B detects SF, as shown in FIG. 24. The station A performs bridge control in regard to the line specified by the K1 byte (switch request) that has been received. Bridge control is control for sending identical signals to both working and protection channels. After performing bridge control, the station A transmits the K2 byte (switch response), which is in response to the received K1 byte, to the opposite station (station B). Upon receiving the K2 byte, the station B performs switch control. Switch control is control for switching a designated line signal in the receiving direction to a protection channel.
In the case of the bidirectional mode, the K1 byte (switch request) is sent to station A if station B detects SF, as shown in FIG. 24B. Station A performs bridge control in regard to the line specified by the K1 byte (switch request) that has been received, sends back the K2 byte (switch response) in the same manner as in the unidirectional mode and, at the same time, sends the K1 byte designating "reverse request" (RR). Upon receiving RR, station B performs switch control and bridge control in regard to the line that was designated by the K1 byte sent by the B station itself and sends the K2 byte (switch response) to the opposite station (station A). Upon receiving the K2 byte, station A performs switch control.
FIG. 25 is a diagram showing the construction of a wireless transmission apparatus according to the prior art. The apparatus includes a baseband processing unit (BB) 21 which executes baseband processing such as processing for interfacing an SDH transmission line and processing for inserting/extracting overhead, a transceiving unit 22 having transmitters TX.sub.W, TX.sub.P in working and protection routes, respectively, as well as receivers RX.sub.W, RX.sub.P in the working and protection routes, respectively, and a switch 23, which is for switching between the working and protection routes, having a transmitter changeover switch SW.sub.T and a receiver changeover switch SW.sub.R.
FIG. 26 illustrates the transmitting route or receiving route of the wireless transmission apparatus, which is depicted in FIG. 25, when expressed in the form of function blocks. Numerals 24, 25 denote functional sections on the wired and wireless sides, respectively. The functional section 24 on the wired side includes an SDH physical interface SPI, a regenerator section termination RST, a multiplex section termination MST, and a multiplex section adaptation MSA. The functional section 25 on the wireless side includes a multiplex section adaptation MSA, a multiplex section termination MST, a regenerator section termination RST, working and protection radio SDH physical interfaces RSPI, and radio protection switching RPS for switching between working and protection channels by controlling the switch 23 (FIG. 25) in response to failure in a wireless channel.
When a wireless channel fails in the wireless transmission apparatus according to the prior art, only the wireless side can be changed over synchronously without instantaneous disconnection by the switch 23 provided on the wireless side. Since the wired side is not changed over owing to the failure in the wireless channel, there is no change in the channel identifier used when the host device is notified of the supervisory information on the wired side. This is advantageous in that management is facilitated. With the wireless transmission apparatus according to the present invention, however, the baseband processing unit, working transmitter TX.sub.W, protection transmitter TX.sub.P, working receiver RX.sub.W and protection receiver RX.sub.P are individual units that are formed on separate boards. A problem that arises is large size and high cost.
Accordingly, there has been proposed a wireless transmission apparatus in which the baseband processor, modulator/demodulator and transceiver have been unified (consolidated into one unit) to the maximum extent in order to lower the cost of the hardware and conserve space. FIG. 27 is a block diagram illustrating such a wireless transmission apparatus. The apparatus includes units K.sub.1 -K.sub.n, K.sub.p each obtained by unifying a baseband processor, modulator/demodulator and transceiver. The units K.sub.1 -K.sub.n are working units provided for corresponding working channels 1-n, and the unit K.sub.p is a protection unit provided for a corresponding protection channel. The apparatus further includes a receiving filter & antenna duplexer BR; an antenna ANT; sending-end and receiving-end changeover switches SW.sub.1 -SW.sub.n provided on the transmission-line side of the working units K.sub.1 -K.sub.n, respectively, for changing over between working and protection units; and a supervisory controller SV having a function for supervising the status of each unit, a function for working/protection switching control (channel control) in response to occurrence of failure, a function for supplying a timing clock and an order wire communication method. FIG. 28 is a block diagram showing the functions of the wireless transmission apparatus illustrated in FIG. 27. Components identical with those shown in FIG. 27 are designated by like reference characters. Numerals 24, 25 denote the functional sections on the wired and wireless sides, respectively. The apparatus includes radio protection switching RPS for switching between working and protection units by controlling the switches SW.sub.1 -SW.sub.n in accordance with predetermined logic, SDH physical interfaces SPI, regenerator section terminations RST, multiplex section terminations MST, multiplex section adaptations MSA and radio SDH physical interfaces RSPI.
The wireless transmission apparatus of FIG. 27 is advantageous in that the cost of hardware is less and more space is conserved in comparison with the wireless transmission apparatus of FIG. 25. However, since the changeover switches are provided at a position opposite from the wireless side, it is difficult to synchronize the working and protection signals and perform switching without instantaneous disocnnection at the time of switching. (Synchronization is performed by the RSPIs.)
Thus, with the first wireless transmission apparatus (FIG. 25) according to the prior art, a signal processor on the transmitting side for receiving a baseband signal, modulating the signal and converting the signal to a radio frequency and a signal processor on the receiving side for, conversely, receiving a radio-frequency signal, demodulating the signal and transmitting the signal as a baseband signal are constructed as individual units on a per-block basis. However, in order to reduce size and lower cost with modern large-capacity wireless apparatus (STM1-level, 156M wireless transmission apparatus, etc.), it is so arranged that all or part of both the signal processor on the transmitting side and signal processor on the receiving side be packaged as a single unit as in the second wireless transmission apparatus (FIG. 27) according to the prior art. Consequently, though switching can be performed without instantaneous disconnection at occurrence of an error in a wireless channel with the arrangement of FIG. 25, the arrangement of FIG. 27 in which the processors are consolidated requires that switching be performed outside the unit, thereby making it difficult to perform switching without instantaneous disconnection.
Further, in a case where the transmitting processor and the receiving processor are included in one unit as in the second wireless transmission apparatus of the prior art, it is necessary to switch both sent and received signals to the protection unit K.sub.p when a working unit is replaced. In general, however, in order to reduce line interruption due to switching, line switching is carried out by switching the transmitting side and receiving side separately. When the unit is replaced, therefore, it is necessary to perform switching manually on each side. The result is a troublesome unit switching operation.
Furthermore, even if a failure develops in a wireless channel, the second wireless transmission apparatus is such that the function blocks on the wired side also are changed over at the same time. As a consequence, even the identifier of supervisory information on the wired side that originally has no relation to the failure is changed, and the host monitoring device must be aware of both supervision on the wired side and changeover on the wireless side. In case of network supervision, a transmission line can be regarded as a single end-to-end pipe without taking into account the transmission medium (see transmission lines 1 and 2 in FIG. 29). Accordingly, even though working/protection unit changeover is performed within a wireless apparatus, data flows through the same transmission path (transmission paths 1 and 2 in FIG. 29) as far as the network is concerned. However, with the wireless transmission apparatus of FIG. 27, the protection and working channels are regarded as different transmission channels and the supervisory information of the working units and protection unit is regarded as the supervisory information of different transmission channels. Therefore, if working unit K.sub.1 is switched over to protection unit K.sub.p, as shown in FIG. 30, the supervisory controller SV shown in FIG. 31 sends the status information of working unit K.sub.1 to a host device OPS as information of transmission line 1 before the unit changeover but sends the status information of protection unit K.sub.p to a host device OPS as information of transmission line 0 after the changeover to the protection unit K.sub.p is made. In other words, the identifier is changed before and after the working/protection unit changeover and then the status information is reported to the host device. This means information detected from a working unit and information detected from a protection unit must each be managed (output) separately. As a result, the network manager must have knowledge of a changeover state that is specific to the wireless medium.